1. Field of the Invention
The instant invention relates to a process for recovering the alkanolamines from the reclaimer bottoms of an acid gas scrubbing process wherein an alkanolamine absorption solution is utilized to absorb an acid gas, i.e. CO.sub.2 from a gas stream and said absorption solution is regenerated by desorption of the CO.sub.2 therefrom at conditions which result in a portion of the alkanolamine being converted into a 2-oxazolidinone.
2. Description of the Art
The removal of acid gases such as H.sub.2 S, CO.sub.2, COS and the like from natural and synthetically-produced gases, including hydrogen, to improve their quality is a widely practiced technology employing many different processes based on chemical reactant and physical absorption characteristics of these acid gases with both liquids and solids. However, one of the most widely used processes employs alkanolamines alone or in combination with one or more chemical reactants or physical absorbents such as sulfolane. These products of the reaction as well as the absorbents of course must be regenerated, freed of the acid gas, and reused to absorb the acid gases from the natural or synthetic gas in a cyclical or continuous process. During regeneration, some of the alkanolamines undergo cyclization in the presence of and in reaction with CO.sub.2 to the corresponding 2-oxazolidinone, which is difficult to convert back to the alkanolamine. The so-formed 2-oxazolidinone is a cyclic carbamate, which does not react with acid gases and therefore creates a waste product of unusable heavy materials which must be purged from the system to prevent their build-up.
U.S. Pat. No. 3,658,462 addresses itself to a process to regenerate the alkanolamines by hydrolysis in the presence of an inorganic base. However, in this process, 1 mole of inorganic carbonate per mole of waste oxazolidinone processed is formed. Thus, although the waste product is regenerated into the alkanolamines, the inorganic carbonate creates a separation and disposal problem.
In a similar fashion, UK Pat. No. 1,118,687 describes contacting alkanolamine-containing waste streams from acid gas purification processes with sufficient of an alkaline-reacting potassium compound, e.g., KOH, to cause separation into a purified amine-rich phase and an aqueous potassium salt containing phase.
French Brevet No. 2,382,922 addresses the same problem of recovering alkanol amines from oxazolidinone-containing acid gas treatment solutions, by heating such solutions in the presence of water at elevated temperature and pressure, e.g., 200.degree.-300.degree. C. and 10-60 atmospheres. U.S. Pat. No. 4,138,468 also describes the recovery of alkanolamines from acid gas treating solutions by heating at 140.degree.-200.degree. C. in the presence of a gross stoichiometric excess of water for an extended period of time, and generally at an elevated pressure. These patents do not utilize an inorganic base to convert the oxazolidinone into the alkanolamine precursor; however, the rate of conversion is slow and a long induction period is required before the conversion begins.
U.S. Pat. No. 4,281,200 somewhat overcomes the shortcomings of the above two approaches to recovering the alkanolamine from an oxazolidinone-containing solution, i.e. the problem of disposal of the salt obtained during the inorganic base catalyzed conversion of oxazolidinone into alkanolamine and the slow reaction rate and long induction period of the water hydrolysis of oxazolidinone in the absence of inorganic base. The process described in U.S. Pat. No. 4,281,200 still requires the addition of inorganic base to the oxazolidinone-containing residue; however, the inorganic base is added in a small but catalytic amount.
It would be advantageous to have a process for converting oxazolidinones into their alkanolamine precursors, without adding any inorganic materials, and not requiring long residence times or induction periods.
It is therefore one object of this invention to provide a process for recovering alkanolamines from oxazolidinone compounds by the inorganic, base-free hydrolysis of said oxazolidinone compounds.
It is another object of this invention to provide a process to recover alkanolamines from corresponding oxazolidinones wherein said process does not require long residence times or induction periods.
It is another object of this invention to optimize the balance between the rate of conversion of the oxazolidinone to the corresponding alkanolamine and the selectivity to such alkanolamine.
Other objects and advantages of the instant invention will become apparent from a careful reading of the specification below.